STRENGTHS:They can't be stomped (or they're strong against it, at least), and they usually appear in large groups.

WEAKNESSES:Fire.

BACKGROUND:Spinies are strange little spike-covered turtles kept as pets by Lakitus. This connects them to the Koopa Troop by association, but they don't necessarily have any strong loyalty to Bowser, especially considering the recent
revolts held by some Lakitus (more details on that when Lakitu is added
to the compendium).
Spinies are usually only found with Lakitus, but ocassionally you'll find
them on their own. In Super Mario RPG Spinies were replaced by Spikesters
and Spikeys. It took me a long time, but I decided to include Spikey and
Spiny as the same species. (Spikester is a stronger, but similar species.)
Admittedly, Spikesters have several different characteristics from Spinies,
but they share the same spikey shell, dark face hidden inside, and similar
colouring, not to mention that both start as "eggs". If new evidence appears
in the future, I may split the two groups up.

EVOLUTION:From SMB through to SMW, Spinies didn't change much at all. They did go from having brown faces to black ones, but otherwise, remained the
same in appearance.
Then, in Super Mario RPG, a drastic change took place. Suddenly, Spinies
were replaced with similar, yet notably different things called Spikeys.
Spikeys stood on their hind legs and had arm-like forelegs, as well as
a somewhat different shell structure from Spinies. However, the two
shared very similar traits, including colouring, spikes, and the fact that
Lakitu keeps them both as pets, so many scientists have chalked the change
up to an unusual, short-term, generation-based mutation. Such
transformations have been seen in species like Little Goombas. Thus the two
are considered one in the same.
In Super Mario 64, Spinies returned to their old selves....albeit in a
much slower version. Though they are now impervious to all attacks, their
slowness makes them virtually harmless in battle.